Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.4.2

4.2.4.2

yadvā asyāvācīnaṃ nābheḥ | tadasyaiṣa ātmanaḥ so 'syaiṣa āyureva tasmādanayā gṛhṇātyasyai hi sthālī bhavati sthālyā hyenaṃ gṛhṇātyajarā hīyamamṛtājaraṃ hyamṛtamāyustasmādanayā gṛhṇāti

Now, what part of him there is below the navel, that part of his self, that vital energy of his, is this (Dhruva): hence he draws it by means of this (earth), because of her is the bowl (sthâlî), and with a bowl he draws it;--for undecaying and immortal is this (earth), and undecaying and immortal is the vital energy: therefore he draws it by means of this (earth).